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    SubjectRe: [PATCH v3 00/23] ldisc fixes
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    [--cc Alan Cox]

    On Tue, 2013-03-05 at 21:50 +0100, Sebastian Andrzej Siewior wrote:
    > * Peter Hurley | 2013-02-05 15:20:15 [-0500]:
    >
    > > Please re-test with your dummy_hcd/g_nokia testcase, although
    > > I'm not convinced that usb gadget is using tty_hangup() appropriately.
    > > tty drivers use this for async carrier loss coming from an IRQ
    > > which will be disabled if the tty has been shutdown. Does gserial
    > > prevent async hangup to a dead tty in a similar fashion?
    >
    > Not sure I understood. tty_hangup() is only called from within
    > gserial_disconnect() which calls right after usb_ep_disable(). After
    > usb_ep_disable() no further serial packets can be received until the
    > endpoints are re-enabled. This happens in gserial_connect().

    That's why I asked. There are two potential issues:

    First, tty_hangup() is asynchronous -- ie., it returns immediately. It
    does not wait for the tty device to actually perform the hangup. So if
    the gadget layers start cleanup immediately after, expecting that they
    won't get a flurry of tty calls, that would be bad.

    tty_vhangup() is synchronous -- ie., you wait while it cleans up. This
    is what the usb serial core does on it's disconnect() method. But I
    didn't research further if the circumstances were the same.

    Second, when the hangup actually does run -- in __tty_hangup() -- it
    expects the tty to exist. I didn't go looking through the gadget layers
    to see if the tty was disposed some other way, which might race the
    asynchronous tty hangup.

    Thanks,
    Peter Hurley





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